Heat exchanger

ABSTRACT

There is provided a heat exchanger comprising: a housing comprising: an inlet at a proximal end for receiving a first fluid; and an outlet, downstream of the inlet at the distal end of the housing, through which the fluid is configured to exit the housing; and a plurality of heat exchanger cores within the housing, wherein the plurality of heat exchanger cores meet at a junction and diverge from each other towards one of the inlet or the outlet of the housing; wherein the plurality of heat exchanger cores comprises a plate fin arrangement; and, wherein the plurality of heat exchanger cores comprise one or more first flow paths through which the first fluid can pass through the heat exchanger cores, in use.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger, preferably but not exclusively for use in an aircraft.

BACKGROUND

In the aviation engineering, heat exchangers have a fundamental role in the thermal management of various components in the aircraft to ensure that they operate within their designs operating ranges.

Heat exchangers may be used to increase or decrease the temperature of fuel during a flight to increase the efficiency of fuel use within the aircraft engines.

The design process of next generation aerospace heat exchangers faces an increased heat rejection demand. At moderate flight speeds, heat from the systems of aviation engines, lubricants, and different equipment and optional energy systems will often be rejected into air. At relatively high-speeds, heat from these components is often rejected into another heat sink, such as the fuel of the aircraft.

The design of heat exchangers in the aircraft should comply with the constructional requirements of the aircraft, e.g. installation volume, pressure drop, heat duty. Further, many aircraft have strict weight and size requirements and it is a challenge to provide a relatively lightweight and space efficient heat exchanger that is capable of providing the required cooling to the components of the aircraft. Furthermore, traditional heat exchangers that are exposed to incoming air may also have a negative effect on the amount of drag on the aircraft.

The development of new kinds of heat exchangers is ever in progress, both for seeking to reduce the volume of the heat exchanger and to enhance the performances in terms of pressure drop and heat transfer capacity.

The heat exchanger of this disclosure seeks to address some of these above-mentioned problems.

SUMMARY

According to one example, there is provided a heat exchanger comprising:

-   -   a housing comprising: an inlet at a proximal end for receiving a         first fluid; and an outlet, downstream of the inlet at the         distal end of the housing, through which the fluid is configured         to exit the housing; and a plurality of heat exchanger cores         within the housing, wherein the plurality of heat exchanger         cores meet at a junction and diverge [from each other] towards         one of the inlet or the outlet of the housing, wherein the         plurality of heat exchanger cores comprise one or more first         flow paths through which the first fluid can pass through the         heat exchanger cores, in use.

Heat Exchangers are traditionally the biggest components within a thermal Management system. The provision of the diverging cores results in a relatively small and lightweight installation volume compared to other installations whilst simultaneously having same/better thermal performance than inclined or “traditional” cuboid installation. Further the relatively low first fluid pressure losses minimises the overall drag, whilst still delivering the cooling first fluid without the need for motivators.

The provision of a heat exchanger with diverging heat exchanger cores reduces the pressure drop of a first fluid flowing through the heat exchanger, whilst still providing a high level of heat transfer. Reducing the pressure drop results in a reduction of drag on the aircraft. The heat exchanger may be located within ductwork within an aircraft (with a vent to the air) or alternative coupled to an outer skin of the aircraft.

The housing may comprise a substantially square-shaped cross section. In other words, the housing may be substantially cuboid shaped with an opening at a proximal end and an opening at the distal end.

A length of the heat exchanger is approximately four times the length of a width of the heat exchanger. The length of the heat exchanger is the distance between the distal end and proximal end of the heat exchanger along the longitudinal axis of the heat exchanger. The width of the heat exchanger is the distance between walls of the housing in a direction perpendicular to the longitudinal axis of the housing.

In one example, each of the plurality of heat exchanger cores comprises a core inlet for receiving a second fluid and a core outlet through which the second flow is configured to exit the heat exchanger core.

In one example, the core inlet of the heat exchanger core is arranged towards the distal end of the housing. In another example, the core inlet of the heat exchanger is arranged towards the proximal end of the housing. In one example, the core inlet of the heat exchanger is arranged at the junction of the heat exchanger cores.

In one example, the outlet of the heat exchanger core is arranged at the junction of the heat exchanger cores. In other examples, the core outlet of the heat exchanger is arranged towards the proximal end of the housing. In one example, the core outlet of the heat exchanger is arranged at the junction of the heat exchanger cores.

The heat exchanger according to any one of the preceding claims, wherein the heat exchanger cores diverge from each other at an angle of between 60 to 160 degrees.

In one example, the heat exchanger core comprises a finned tube arrangement. In another example, the heat exchanger core comprises a plate-fin arrangement. The heat exchanger core may comprise a plurality of layers.

In one example, the heat exchanger comprises one or more aerofoils configured to guide the flow of the first fluid.

In one example, the heat exchanger cores diverge from each other towards the inlet of the housing. In another example, the heat exchanger cores diverge from each other towards the outlet of the housing.

In one example, the weight of the heat exchanger is between 9 kg to 12 kg. This is compared with a weight of 25 kg to 30 kg for a traditional heat exchanger with a similar heat transfer performance. A heat exchanger with an inclined heat exchanger core that achieves a similar heat transfer performance would weigh approximately 18 kg to 21 kg.

In one example, the plurality of heat exchanger cores comprises two heat exchanger cores.

According to another example, there is provided an aircraft comprising the heat exchanger as described above.

According to another example, there is provided a heat exchanger comprising: a housing comprising: an inlet at a proximal end for receiving a first fluid; and an outlet, downstream of the inlet at the distal end of the housing, through which the fluid is configured to exit the housing; and a plurality of heat exchanger cores within the housing, wherein the plurality of heat exchanger cores meet at a junction and diverge [from each other] towards one of the inlet or the outlet of the housing, wherein the plurality of heat exchanger cores comprises a plate fin arrangement; and, wherein the plurality of heat exchanger cores comprise one or more first flow paths through which the first fluid can pass through the heat exchanger cores, in use.

Heat Exchangers are traditionally the biggest components within a thermal Management system. The provision of the diverging cores results in a relatively small and lightweight installation volume compared to other installations whilst simultaneously having same/better thermal performance than inclined or “traditional” cuboid installation. Further the relatively low first fluid pressure losses minimises the overall drag, whilst still delivering the cooling first fluid without the need for motivators.

The provision of a heat exchanger with diverging heat exchanger cores reduces the pressure drop of a first fluid flowing through the heat exchanger, whilst still providing a high level of heat transfer. Reducing the pressure drop results in a reduction of drag on the aircraft. The heat exchanger may be located within ductwork within an aircraft (with a vent to the air) or alternative coupled to an outer skin of the aircraft.

The housing may comprise a substantially square-shaped cross section. In other words, the housing may be substantially cuboid shaped with an opening at a proximal end and an opening at the distal end.

A length of the heat exchanger is approximately four times the length of a width of the heat exchanger. The length of the heat exchanger is the distance between the distal end and proximal end of the heat exchanger along the longitudinal axis of the heat exchanger. The width of the heat exchanger is the distance between walls of the housing in a direction perpendicular to the longitudinal axis of the housing.

In one example, each of the plurality of heat exchanger cores comprises a core inlet for receiving a second fluid and a core outlet through which the second flow is configured to exit the heat exchanger core.

In one example, the core inlet of the heat exchanger core is arranged towards the distal end of the housing. In another example, the core inlet of the heat exchanger is arranged towards the proximal end of the housing. In one example, the core inlet of the heat exchanger is arranged at the junction of the heat exchanger cores.

In one example, the heat exchanger core is arranged in a counterflow arrangement with respect to the first fluid.

In one example, the outlet of the heat exchanger core is arranged at the junction of the heat exchanger cores. In other examples, the core outlet of the heat exchanger is arranged towards the proximal end of the housing. In one example, the core outlet of the heat exchanger is arranged at the junction of the heat exchanger cores. In one example, the outlets of the plurality of heat exchanger cores may exit the housing through a single aperture.

The heat exchanger cores may diverge from each other at an angle of between 60 to 160 degrees.

The heat exchanger core may comprise a plurality of layers.

In one example, the heat exchanger comprises one or more aerofoils configured to guide the flow of the first fluid.

In one example, the heat exchanger cores diverge from each other towards the inlet of the housing. In another example, the heat exchanger cores diverge from each other towards the outlet of the housing.

In one example, the weight of the heat exchanger is between 9 kg to 12 kg. This is compared with a weight of 25 kg to 30 kg for a traditional heat exchanger with a similar heat transfer performance. A heat exchanger with an inclined heat exchanger core that achieves a similar heat transfer performance would weigh approximately 18 kg to 21 kg.

In one example, the plurality of heat exchanger cores comprises two heat exchanger cores.

According to another example, there is provided an aircraft comprising the heat exchanger as described above.

It will be appreciated that features described in relation to one aspect of the present invention can be incorporated into other aspects of the present invention. For example, an apparatus of the invention can incorporate any of the features described in this disclosure with reference to a method, and vice versa. Moreover, additional embodiments and aspects will be apparent from the following description, drawings, and claims. As can be appreciated from the foregoing and following description, each and every feature described herein, and each and every combination of two or more of such features, and each and every combination of one or more values defining a range, are included within the present disclosure provided that the features included in such a combination are not mutually inconsistent. In addition, any feature or combination of features or any value(s) defining a range may be specifically excluded from any embodiment of the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of an aircraft;

FIG. 2 shows an example of a housing of a heat exchanger;

FIG. 3 shows an example of a known heat exchanger;

FIG. 4 shows a perspective view of an example of a heat exchanger;

FIG. 4A shows an example of the outside of the chamber with a payload on the outside of the chamber;

FIG. 5 shows a cross-sectional view through the heat exchanger of FIG. 4 ;

FIG. 6 shows a perspective view of an example of a heat exchanger;

FIGS. 7A and 7B shows an example of part of a heat exchanger core; and

FIGS. 8A and 8B shows an example of part of a heat exchanger core;

DETAILED DESCRIPTION

FIG. 1 shows an example of an aircraft 100 having fuselage 102. Aircraft 100 are well-known in the art and further details of the aircraft have not been provided here. In one example, the aircraft comprises a high-altitude long endurance (HALE) unmanned aircraft. HALE aircraft typically have long wingspans and low drag to improve their ability to operate efficiently for weeks or months at altitudes in excess of 15 km. In some examples, HALE aircraft include one or more payloads comprising electronic components, such as sensors that require thermal management.

FIG. 2 shows an example of a housing 104 of a heat exchanger. The housing 104 comprises walls 106 configured to provide an enclosure to house a plurality of heat exchanger cores, which will be discussed in more detail below. The enclosure may be open at opposite ends, as will be discussed in more detail below.

In this example, the heat exchanger housing 104 comprises an inlet 108 and an outlet 110 or exit. The inlet 108 is configured to receive a first fluid, such as on- coming air, that may be used as the coolant within the heat exchanger. The outlet 110 is configured to allow the first fluid to exit the heat exchanger after it has passed through the heat exchanger. The inlet 108 of the heat exchanger housing 104 is also the inlet of the heat exchanger. The outlet 110 of the heat exchanger is also the outlet of the heat exchanger.

In the example of FIG. 2 , the housing 104 is a cuboid with open, opposite ends defining the inlet 108 and the outlet 110 respectively. The housing 104 may extend along and define a longitudinal axis A-A. In the example of FIG. 2 , the cross-section of the housing 104, taken perpendicular to the longitudinal axis A-A, would be square-shaped. In other examples, the housing 104 may be cylindrical or have other shapes that extend along a longitudinal axis A-A. For example, the housing 104 of the heat exchanger may be a circular duct.

The housing 104 is shaped so as to be relatively compact, whilst still providing sufficient space for the heat exchanger to be effective. In one example, the housing 104 has a length along the longitudinal axis, A-A, of between 0.5 m and 1.5 m, more preferably 0.8 m to 1.2 m, more preferably 1 m.

The width and height of the housing 104, e.g. the dimensions perpendicular to the longitudinal axis A-A, may be between 0.15 m and 0.3 m, more preferably 0.23 m. The length of the housing 104 may be approximately four times larger the width/height of the housing 104

In one example, the housing walls 106 have one or more apertures (not shown) for receiving a second fluid, as will be discussed in more detail below.

FIG. 3 shows an example of a traditional cuboid arrangement of a heat exchanger that is not within the scope of this invention. In this example, the heat exchanger comprises a core 114 formed of alternating layers 112 a, 112 b. The alternating layers comprise alternating layers of first fluid paths 112 a and second fluid paths 112 b.

In this example, a first fluid flows through the first fluid paths 112 a and a second fluid flows through the second fluid paths 112 b. The first fluid and second fluid are configured to enter the heat exchanger at different temperatures such that heat is exchanged between the first fluid and the second fluid.

The first fluid enters the core 114 in a first direction as indicated by the first arrow B, which in this example is in the direction of the longitudinal axis of the core 114. The first fluid then travels through the core 114 and exits the core as shown by the arrow C. The second fluid enters the core 114 in a second direction, which in this example is perpendicular to the longitudinal axis of the core 114, as shown by arrow D. The second fluid exits the core as indicated by arrow E.

In this example, the first fluid is blocked off from travelling through the second fluid paths 112 b and the second fluid is blocked off from travelling through the first fluid paths 112 a.

The blockage of the first fluid flow path using the traditional cuboid installation results in a large pressure drop in the first fluid flow as it enters the heat exchanger. This pressure drop then causes increased drag of the overall drag and might require flow motivators. In addition, this installation results in small frontal area for the first fluid flow path, requiring a fin structure and thus resulting in high installation volume and weight. In other words, the traditional cuboid installation shown in FIG. 3 is undesirable as it has many drawbacks.

FIG. 4 shows a heat exchanger 120 according to the present invention. In this example, the heat exchanger 120 comprises the housing 104 as shown in FIG. 2 . For clarity, the housing is shown as transparent in FIG. 4 so the elements within the housing 104 are visible.

As with FIG. 2 , the housing 104 has an inlet 108 for receiving the first fluid and an outlet 110, downstream of the inlet 108, through which the first fluid is configured to exit the housing 104. In one example, the inlet 108 of the housing 104 is arranged at a proximal end of the housing 104 and the outlet 110 is arranged at a distal end of the housing 104. In another example, the inlet 108 is arranged at the distal end of the housing 104 and the outlet is arranged at the proximal end of the housing 104. For clarity, the longitudinal axis A-A has not been overlaid on the FIG. 4 , but it is shown in FIG. 2 .

In use, the first fluid is configured to flow from the inlet 108 to the outlet 110 within the housing 104.

The heat exchanger 120 comprises a plurality of heat exchanger cores 122. In this example, the heat exchanger comprises two heat exchanger cores 122.

The heat exchanger cores 122 are arranged between the inlet 108 and the outlet 110 of the housing 104 of the heat exchanger 120. That is to say that the first fluid must flow through at least one of the heat exchanger cores 122 when travelling from the inlet 108 to the outlet 110 of the heat exchanger 120.

The heat exchanger cores 122 comprises a first fluid path, through which the first fluid can travel. The heat exchanger cores 122 also comprise a second fluid path through which a second fluid can travel. The first fluid path and the second fluid path are isolated from each other to prevent mixing of the first fluid and the second fluid. For example, the second fluid may travel within pipes of the heat exchanger core 122 whilst the first fluid is configured to flow in a path around the pipes of the heat exchanger core 122.

The heat exchanger cores are angled with respect to the longitudinal axis A-A of the housing 104. Put another way, the heat exchanger cores 122 are not parallel with the longitudinal axis A-A of the housing 104.

In the example shown in FIG. 4 , the heat exchanger cores 122 meet or join at a junction 124 within the housing 104 of the heat exchanger 120. In this example, the heat exchanger cores 122 diverge from the junction 124 towards the outlet 110 of the housing 104 of the heat exchanger 120. That is to say that the distance between the heat exchanger cores 122 increases from the junction 124 towards the outlet 110.

In FIG. 4 , the heat exchanger 120 comprises two heat exchanger cores 122, but more than two heat exchanger cores 122 may be used in practice.

The heat exchanger core 122 comprises a core inlet 126 and a core outlet 128. The core inlet 126 is configured to receive a second fluid. The second fluid is configured to leave the heat exchanger core 122 through the core outlet 128.

In FIG. 4 , the wall 106 of the housing 104 comprises an aperture through which the second fluid can enter into the core inlet 126. In this arrangement, the second fluid would still be isolated from the first fluid as the second fluid would enter directly into a conduit or pipe of the heat exchanger core 122 that is isolated from the first fluid.

An additional aperture may be present in the walls 106 of the housing 104 for the core outlet 128 to allow the second fluid to exit the heat exchanger 120.

In the example shown in FIG. 4 , the core inlets 126 are arranged perpendicular to the longitudinal axis A-A of the housing 104 of the heat exchanger 120, but other arrangements are possible. The core inlets 126 may be arranged towards or adjacent to the inlet 108 or outlet 110 of the housing 104. In the example shown in FIG. 4 , the core inlets are shown towards or adjacent to the outlet 110 or distal end of the housing 104, but in other arrangements they may be located towards or adjacent to the inlet 108 or proximal end of the housing 104. In both examples, the heat exchanger cores 122 still diverge from the junction 124 towards the inlet 108 or the outlet 110 of the housing 104.

The core outlet 128 may be arranged at or adjacent to the junction 124. The core outlet 128 may be arranged to be perpendicular to the longitudinal axis A-A of the housing 104. In one example, the core outlet 128 is configured to be perpendicular to the core inlets 126. In other examples, the core inlets 126 and core outlet 128 may be reversed from those shown in FIG. 4 . In other words, the second fluid may enter the heat exchanger core 122 at the core inlet 126, which is located at or approximate to the junction 124 and the second fluid then travels through the heat exchanger core 122 towards the core outlet 128, which may be located at or towards the inlet 108 or outlet 110 of the housing 110 (e.g. a counterflow arrangement with respect to the first fluid).

As shown in FIG. 4 , the core inlets 126 of each of the heat exchanger cores 122 may be opposite to each other. That is to say that they are arranged on the opposite sides of the housing 104 relative to each other. The core outlets 128 of the heat exchanger cores 122 are arranged adjacent to each other. In one example where the respective core outlets 128 of the heat exchanger cores 122 are arranged adjacent to each other, both outlets 128 may exit the housing 104 through a single aperture. In this way, apertures into the housing 104 are minimised. This makes the heat exchanger 120 simpler to manufacture.

In FIG. 4 , the first fluid flow enters the heat exchanger 120 via the inlet 108 in the direction represented by arrow F, i.e. substantially parallel to the longitudinal axis A-A of the housing 104. The first fluid then passes through one or more first flow paths of the heat exchanger cores 122 before exiting the housing 104 at the outlet 110. The first fluid flow exits the heat exchanger 120 in the direction indicated by arrow G in FIG. 4 .

In FIG. 4 , a second fluid enters the heat exchanger 120 via core inlets 126. The second fluid may enter the heat exchange cores 122 in the direction indicated by arrows H in FIG. 4 .

The second fluid then travels within the heat exchanger core 122 and exits the heat exchanger core 122 at the core outlet 128. In FIG. 4 , the second fluid exits the heat exchanger cores 122 in the direction indicated by arrow I in FIG. 4 .

One or more headers (not shown) may be present at the core inlets 126 and/or core outlets 128.

In FIG. 4 , the core inlets 126 are shown substantially at or adjacent to the outlet 110 of the housing 104. In other words, the core inlets 126 may be located at or adjacent to the distal end of the housing 104.

However, in other examples, there may be a gap between the core inlet 126 and the distal end of the housing 110.

FIG. 5 shows a cross-sectional view of the heat exchanger 120. As shown in FIG. 5 , the heat exchanger cores 122 may have the same shape but are handed about the longitudinal axis A-A of the housing.

FIG. 5 also shows a plurality of flow guide vanes 130 within the heat exchanger 120. The flow guide vanes 130 may extend the full height of the heat exchanger 120.

The purpose of the flow guide 130 vanes to is guide the first fluid to flow through the heat exchanger cores 122 at an optimum angle, ensuring even mass flow distribution across the frontal area of the heat exchanger core.

The junction 124 at which the heat exchanger cores 122 meet may be on the longitudinal axis A-A of the housing. That is to say that the junction may be on a central line, when viewed from above, of the housing 104.

The junction 124 may be spaced from the inlet 108 of the housing 104. In one example, the junction 124 spaced at approximately half the width of the housing 104 from the inlet.

The heat exchanger cores 122 may be shaped such that the inlet 126 is arranged at an approximate 45-degree angle to the longitudinal axis A-A of the housing 104. The heat exchanger cores 122 has internal length K, which represents the length of the inside portion of the heat exchanger core 122, e.g. the boundary of the heat exchanger core 122 that faces the other heat exchanger core. The heat exchanger core 122 also has an external length L, which represents the length of the outside portion of the heat exchanger core 122, e.g. the boundary of the heat exchanger core 122 that faces the wall 106 of the housing 104.

FIG. 5 also shows a width J, which is the dimension perpendicular to the longitudinal axis A-A at the core inlet 126.

In the example shown in FIG. 5 , the heat exchanger cores 122 are configured to diverge at an angle denoted by α. A key design constraint of the heat exchanger 122 is to keep the external length L and the width J to a minimum for a specific heat duty/pressure drop. This allows the angle α to be designed to be sufficiently high, so fewer or no flow guiding vanes 130 are required to guide the first fluid flow through the heat exchanger 120. Providing fewer flow guiding vanes 130 reduces the weight of the heat exchanger 120 and makes the design of the heat exchanger 120 easier.

Preferably, the angle α is between 60 to 160 degrees, more preferably between 75 degrees to 145 degrees, more preferably between 90 degrees to 130 degrees, more preferably between 105 degrees to 115 degrees. Providing the diverging angle α of between 60 to 160 degrees reduces the pressure drop of the first fluid within the heat exchanger 120 by providing a relatively larger cross-sectional area of the air side versus the flow length.

Further, the diverging heat exchanger cores 122 maximises the frontal area for the first fluid compared with other arrangements of heat exchangers cores. This leads to a lower pressure drop on the first fluid side and/or allows to use more heat transfer efficient geometries. This arrangement means that the heat exchanger 120 can employ more efficient (heat transfer wise) geometries for the first fluid exchanger side (e.g. the inlet 108 of the housing 104).

This arrangement also provides a reduced weight of heat exchanger 120. In one example, the heat exchanger 120 is approximately 50-60% lower than “traditional” installations (e.g. the arrangement shown in FIG. 3 ).

There are interesting counter/cross orientation of the first fluid flow and the second fluid flow in this diverging arrangement to bring thermal benefits too.

In one example, the geometry of the heat exchanger core 122 is as follows:

0.05x≤J≤0.35x

0.8y≤L≤1.2y

Here x and y are the width and length of the housing 104, respectively.

The sizes of other components (such as headers) within the heat exchanger 120 should be kept to a minimum to keep the weight in the heat exchanger 120 down.

The arrangement of the diverging heat exchanger cores 122 provides minimises the first fluid pressure drop through reducing the local Reynolds number inside the heat exchanger 120.

FIG. 6 shows an alternative arrangement of the heat exchanger core 122 compared with the example shown in FIG. 4 . For clarity, the housing 104 is shown as transparent in FIG. 6 so the elements within the housing 104 are visible.

In this example, the heat exchanger cores 122 still meet at the junction 124. However, the heat exchanger cores 122 then diverge towards the inlet 108 or the proximal end of the housing 104. That is to say that the distance between the heat exchanger cores 122 increases from the junction 124 towards the inlet 108.

In FIG. 6 , the heat exchanger 120 comprises two heat exchanger cores 122, but more than two heat exchanger cores 122 may be used in practice.

The heat exchanger core 122 comprises a core inlet 126 and a core outlet 128. The core inlet 126 is configured to receive a second fluid. The second fluid is configured to leave the heat exchanger core 122 through the core outlet 128.

In FIG. 6 , the wall 106 of the housing 104 comprises an aperture through which the second fluid can enter the core inlet 126. In this arrangement, the second fluid would still be isolated from the first fluid as the second fluid would enter directly into a conduit or pipe of the heat exchanger core 122 that is isolated from the first fluid.

An additional aperture may be present in the walls 106 of the housing 104 for the core outlet 128 to allow the second fluid to exit the heat exchanger 120.

In the example shown in FIG. 6 , the core inlets 126 are arranged perpendicular to the longitudinal axis A-A of the housing 104 of the heat exchanger 120, but other arrangements are possible. In this example, the core inlets 126 are arranged towards or adjacent to the inlet 108 of the housing 104.

The core outlet 128 may be arranged at or adjacent to the junction 124. The core outlet 128 may be arranged to be perpendicular to the longitudinal axis A-A of the housing 104. In one example, the core outlet 128 is configured to be perpendicular to the core inlets 126. In other examples, the core inlets 126 and core outlet 128 may be reversed from those shown in FIG. 6 . In other words, the second fluid may enter the heat exchanger core 122 at the core inlet 126, which is located at or approximate to the junction 124 and the second fluid then travels through the heat exchanger core 122 towards the core outlet 128, which may be located at or towards the inlet 108 or outlet 110 of the housing 110.

As shown in FIG. 6 , the core inlets 126 of each of the heat exchanger cores 122 may be opposite to each other. That is to say that they are arranged on the opposite sides of the housing 104 relative to each other. The core outlets 128 of the heat exchanger cores 122 are arranged adjacent to each other.

In FIG. 6 , the first fluid flow enters the heat exchanger 120 via the inlet 108 in the direction represented by arrow F, i.e. substantially parallel to the longitudinal axis A-A of the housing 104. The first fluid then passes through one or more first flow paths of the heat exchanger cores 122 before exiting the housing 104 at the outlet 110. The first fluid flow exits the heat exchanger 120 in the direction indicated by arrow G in FIG. 6 . A second fluid enters the heat exchanger 120 via core inlets 126. The second fluid may enter the heat exchange cores 122 in the direction indicated by arrows H in FIG. 6 .

The second fluid then travels within the heat exchanger core 122 and exits the heat exchanger core 122 at the core outlet 128. In FIG. 6 , the second fluid exits the heat exchanger cores 122 in the direction indicated by arrow I.

In FIG. 4 , the core inlets 126 are shown substantially at or adjacent to the inlet 110 of the housing 104. In other words, the core inlets 126 may be located at or adjacent to the proximal end of the housing 104.

However, in other examples, there may be a gap between the core inlet 126 and the proximal end of the housing 110. The angle between the heat exchanger cores 122 is the same as described above in relation to FIG. 4 .

The arrangement of the heat exchanger 120 of FIG. 6 provides the same advantages to the arrangement in FIG. 4 . That is to say that the pressure-drop of the first fluid entering the heat exchanger is significantly reduced.

In one example, the first fluid is air or another compressible fluid (gas). The second fluid may be an incompressible fluid, i.e. liquid such as water or oil.

The heat exchanger cores 122 may comprise a finned tube arrangement. FIGS. 7A and 7B show an example of part of heat exchanger core 122 in the form of a finned tube. In this example, the first fluid travels in the direction indicated by arrow M through the heat exchanger core 122. The first fluid travels through one or more first fluid paths through the heat exchanger core 122. The first fluid path may be defined by a plurality of fins 134.

The second fluid travels within the heat exchanger core 122 in conduits 132. The fins 134 are thermally coupled to the conduits 132.

FIG. 7B shows a cross section through the example shown in FIG. 7A, but with only a single tube 132.

The heat exchanger cores 122 comprise a plate fin arrangement. Plate fin heat exchangers comprise a greater density than tube fin arrangements owing to their unique geometry which creates a greater surface area for heat transfer to take place. Therefore, plate fin heat exchangers can be made both smaller and more lightweight for a specified heat load or alternatively can dissipate a higher heat load without increasing in size and/or weight when compared to conventional tube fin heat exchangers. FIGS. 8A and 8B show an example of part of a heat exchanger core 122 in the form of a plate fin arrangement. In this example, there are alternating layers of first fluid paths and second fluid paths. The first fluid may travel in a direction represented by arrow O and the second fluid may travel in a direction represented by arrow P. FIG. 8B shows an example of a cross-section through one of the fluid paths.

Plate fin heat exchangers may also be manufactured using additive manufacturing techniques, for example selective laser melting, selective laser sintering or directed energy deposition. Such manufacturing techniques allow complex plate fin heat exchanger geometries to be manufactured which are otherwise difficult or impossible with conventional manufacturing techniques. As such, plate fin heat exchangers may be manufactured with even greater surface areas than tube fin heat exchangers or conventionally manufactured plate fin heat exchangers thereby allowing the possibility of smaller, more lightweight heat exchangers for a specified heat load or alternatively the ability to dissipate a higher heat load without increasing in size and/or weight.

The heat exchanger 122 provides an increased frontal transfer area, which allows the reduction of the lower Reynolds number inside the heat exchanger 122 compared to traditional cuboid (FIG. 3 ) or inclined installation. This in turn enables the use of more heat transfer efficient internal geometries which allow the reduction in the heat exchanger 122 installation volume and weight (up to 60% when compared to traditional and 40% when compared to the inclined). Additionally, the flow orientation of the first fluid and the second fluid is closer to the most efficient counter-flow in the heat exchangers 120 shown in FIGS. 4 and 6 , compared to a standard cross-flow configuration found in the traditional cuboid or inclined heat exchanger designs, making the heat transfer more efficient and the heat exchanger 120 smaller for a given heat transfer requirement within a certain pressure drop restriction.

Where, in the foregoing description, integers or elements are mentioned that have known, obvious, or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present disclosure, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the disclosure that are described as optional do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, while of possible benefit in some embodiments of the disclosure, may not be desirable, and can therefore be absent, in other embodiments. 

What is claimed is:
 1. A heat exchanger comprising: a housing comprising: an inlet at a proximal end for receiving a first fluid; and an outlet, downstream of the inlet at the distal end of the housing, through which the fluid is configured to exit the housing; and a plurality of heat exchanger cores within the housing, wherein the plurality of heat exchanger cores meet at a junction and diverge from each other towards one of the inlet or the outlet of the housing; wherein the plurality of heat exchanger cores comprises a plate fin arrangement; and wherein the plurality of heat exchanger cores comprise one or more first flow paths through which the first fluid can pass through the heat exchanger cores, in use.
 2. The heat exchanger according to claim 1, wherein the housing comprises a substantially square-shaped cross section.
 3. The heat exchanger according to claim 1, wherein a length of the heat exchanger is approximately four times the length of a width of the heat exchanger.
 4. The heat exchanger according to claim 1, wherein each of the plurality of heat exchanger cores comprises a core inlet for receiving a second fluid and a core outlet through which the second flow is configured to exit the heat exchanger core.
 5. The heat exchanger according to claim 4, wherein core inlet of the heat exchanger core is arranged towards the distal end of the housing.
 6. The heat exchanger according to claim 4, wherein the outlet of the heat exchanger core is arranged at the junction of the heat exchanger cores.
 7. The heat exchanger according to claim 4, wherein the heat exchanger core is arranged in a counterflow arrangement with respect to the first fluid.
 8. The heat exchanger according to claim 1, wherein the heat exchanger cores diverge from each other at an angle of between 60 to 160 degrees.
 9. The heat exchanger according to claim 1, wherein the heat exchanger core comprises a plurality of layers.
 10. The heat exchanger according to claim 1, comprising one or more aerofoils configured to guide the flow of the first fluid.
 11. The heat exchanger according to claim 1, wherein the heat exchanger cores diverge from each other towards the inlet of the housing.
 12. The heat exchanger according to claim 1, wherein the heat exchanger cores diverge from each other towards the outlet of the housing.
 13. The heat exchanger according to claim 1, wherein the weight of the heat exchanger is between 9 kg and 12 kg.
 14. An aircraft comprising the heat exchanger according to claim
 1. 